The present invention is directed to a species-selective pressure gauge with an extended operation of up to 10 Pascal and more. More specifically, the invention is directed to a species selective pressure gauge, such as a U.S. Penning gauge, in which an application of the Penning gauge will accurately analyze optical emission from a cold-cathode discharge.
The application of a cold-cathode ionization gauge, such as a Penning gauge, for neutral gas pressure measurements is known in the art. However, a problem exists in which the application thereof is limited to pressures below 1 Pascal. This problem is commonly overcome by use of alternative gas pressure sensors, such as a capacitance manometer. These alternative gas pressure sensors/gauges are not ionization gauges in that they do not generate an electrical discharge by ionization of the neutral gas. Therefore, even though the pressure of the neutral gas may be measured, the composition of the gas still cannot be accurately determined.
In the case of a species-selective gauge, the light emitted from the electrical discharge is analyzed to determine the composition of the gas. More specifically, the composition of the gas is analyzed to determine the relative concentration of the various gaseous species contained in the gas. Each species emits light at characteristic frequencies (colors) when excited by the electric discharge. As a result, it is essential to have an ionization-type gauge, in order to have a species selective gauge, based on this actinometric technique.
The use of gauges to analyze gas is therefore known. Some publications expressing and explaining the known concepts include U.S. Pat. Nos. 3,622,870; 3,872,377; and 4,000,457; and publications to D. L. Hillis, C. C. Klepper, M. Von Hellermann, J. Ehrenberg, K. H. Finken, G. Mank. xe2x80x9cDeuterium-Tritium Concentration Measurements in the Divertor of a Tokamak via a Modified Penning Gaugexe2x80x9d. Fusion Engineering and Design (1997); K. H. Finken, K. H. Dippel and A. Hardtke. xe2x80x9cMeasurements of helium gas in a deuterium environmentxe2x80x9d. Reviews of Scientific Instruments (1992); C. C. Klepper, D. L. Hillis, M. R. Wade et. al. xe2x80x9cApplication of a Species-Selective Penning Gauge to the Measurement of Neon and Hydrogen-isotope Partial Pressures in the Plasma Boundaryxe2x80x9d. Rev. Sci. Instrum. (1997); and C. C. Klepper, J. T. Hogan, et.al. xe2x80x9cDivertor Neutral Pressure Enhancement with a Baffle in DIII-Dxe2x80x9d, Nucl. Fusion (1993).
Accordingly, a problem still exists in the art whereby it is necessary to determine at least the pressure, and further, the composition, of the neutral gas at pressures above 1 Pascal.
The present invention described herein, solves this problem in the art by extending the upper limit in the pressure range of operation of the species-selective gauge. This is done by continuously adjusting the operational parameters of the cold-cathode ionization gauge to maintain it in a non-saturated mode. If the measurement is done in a process where the gas pressure varies in time, specially designed electronics are employed to maintain the gauge in an operational state, where the optical measurements can be carried out and the calibration is maintained.
Therefore, it is a principal object of this invention to provide a species-selective gauge capable of measuring optical emissions at gas pressures above 1 Pascal.
Another object of the present invention is to provide a species-selective gauge for measuring optical emissions of a cold-cathode ionization gauge at gas pressures above 1 Pascal.
A further object of the invention is to provide a species-selective gauge for maintaining output emissions of a discharge in a non-saturated state.
A still further object of the invention is to provide an apparatus for a species-selective gauge in which a discharge current is monitored in order to correspondingly adjust a voltage applied to a magnetic field.
Yet another object of the invention is to provide an apparatus for a species-selective gauge in which an output of a magnetic field is monitored in order to correspondingly adjust the current input to the electromagnet and thereby maintain a constant current.
These and other objects of the invention are achieved by providing a diagnostic apparatus, which includes a pressure gauge member having an enclosed housing, an anode plate, a pair of cathode plates sandwiching the anode plate, an anode connector at an external surface of the gauge, and a lead connecting the anode plate to the anode connector. Each of the anode plate, pair of cathode plates, and lead are confined within the gauge housing. A power supply is provided for supplying power to the anode connector, the power supply including a positive terminal and a negative terminal. A resistor is connected to each of the positive terminal of the power supply and the anode connector of the gauge member. A pair of electromagnets are positioned adjacent to the gauge member, each electromagnet having a pole piece formed therein for completing a magnetic circuit outside of the gauge. A power amplifier supplies varying power to the electromagnets, and a feedback circuit is connected to the gauge, the power supply, the said power amplifier for proportionally and selectively changing a strength of the electromagnets upon detecting an opposing change in current discharge from the gauge.